For ecigs, I'd rather buy what's designed for the type of vaping I do. For me, that's a Kayfun. It's better left in stock condition. If wanted DTL I'd buy something that's designed to do that.
The design fundamentals between the open Direct Lung vs tighter Mouth-to-Lung draw are basically about airflow, chamber + chimney and juice channels. Kayfun 3.x got lot of the internals right for MTL but I'd like to see those internals / dimensions refreshed in a more modern package.
All my kayfuns are heavily modded and one only has the the base/deck left from the original set. Its puny juice channels just about handle my 50/50 mixes and refills are annoying due to the bottom fill screw and its tiny fill hole, but at 1.2 ohm it is gentle on batteries and flavours are good.
With the ultra-low-ohm poly-coil craze and the current regulation 2 ML tank demands mostly satisfied for the time being I'm hopeful that some manufacturers will again look at their MTL single-coil RTA designs.
Besides dedicated single-coil RTAs there would also be market for better "replaceable" RBAs and other after-market parts for
dual-use units like Kanger's Subtank.
Another quite well-regarded dual-use tank is the Ego One (Mega at 22mm) by Joyetech. Some say the 0.5 ohm RBA piece (called CLR) works for MTL, but the 1 ohm factory coils are very good for the purpose.
Since it's almost December, here's my feature wishlist for the ideal MTL tank:
- dual-use, with good screw-on RBA deck and compatibility with popular quality MTL coils like the Ego One 1 ohms.
- top fill, either plain cap or Crius-type lift-top.
- tight to medium draw AFC. No need for fully open draw setting.
- JFC would be nice but not absolutely crucial if wick wells and juice channels are done right.
- clean, classy and compact design but with
some contours for grip.
- compact 3ml and more spacious 5ml tank options.
- under $/€ 20.